Method of making and using shape memory polymer patches

ABSTRACT

A method of repairing a composite component having a damaged area including: laying a composite patch over the damaged area; activating the shape memory polymer resin to easily and quickly mold said patch to said damaged area; deactivating said shape memory polymer so that said composite patch retains the molded shape; and bonding said composite patch to said damaged part.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation of U.S. Utility application Ser. No. 11/611,184filed Dec. 15, 2006 which is a continuation of U.S. Utility applicationSer. No. 11/569,902 filed Dec. 1, 2006, which is a national stage entryfrom PCT application PCT/US2005/019842 filed Jun. 4, 2005, which allclaim priority benefit of U.S. Provisional Patent Application Ser. No.60/577,003 filed Jun. 4, 2004. Additionally this application is acontinuation of U.S. Utility application Ser. No. 12/090,760 filed Apr.18, 2008, which is a national stage entry from PCT/US2006/062179 filedDec. 15, 2006 which further claims priority from a U.S. ProvisionalPatent Application Ser. No. 60/750,502 filed Dec. 15, 2005.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

This application was made in part with government support under contractnumber NNK05OA29C awarded by the National Aeronautics and SpaceAdministration (NASA). The U.S. government has certain rights in theinvention.

BACKGROUND OF THE INVENTION

1. Patches Background

The present invention generally relates to the repair of components madefrom material such as metals, composites, wood, plastics, glass andother materials. It is to be appreciated that the present invention hasgeneral and specific industrial application in the repair of variousmaterials. The term “composite” is commonly used in industry to identifycomponents produced by impregnating a fibrous material with athermoplastic or thermosetting resin to form laminates or layers.

Generally, polymers and polymer composites have the advantages of weightsaving, high specific mechanical properties, and good corrosionresistance which make them indispensable materials in all areas ofmanufacturing. Nevertheless, manufacturing costs are sometimedetrimental, since they can represent a considerable part of the totalcosts and are made even more costly by the inability to quickly andeasily repair these materials without requiring a complete, andexpensive, total replacement. Furthermore, the production of complexshaped parts is still a challenge for the composite industry. Thelimited potential for complex shape forming offered by advancedcomposite materials leaves little scope for design freedom in order toimprove mechanical performance and/or integrate supplementary functions.This has been one of the primary limitations for a wider use of advancedcomposites in cost-sensitive large volume applications. Additionally,the nature of composite materials does not lend itself to easy repair,especially on cheap, mass produced items and repair kits for moreexpensive, specialty items (such as in the aeronautic industry) arebulky, expensive, and require long time to complete the repair.

Shape memory polymers (SMPs) and shape memory alloys (SMAs) were firstdeveloped about 20 years ago and have been the subject of commercialdevelopment in the last 10 years. SMPs are polymers that derive theirname from their inherent ability to return to their original “memorized”shape after undergoing a shape deformation. SMPs that have beenpreformed can be deformed to any desired shape below or above its glasstransition temperature (T_(g)). If it is below the T_(g), this processis called cold deformation. When deformation of the SMP occurs above itsT_(g), the process is denoted as warm deformation. In either case theSMP must remain below, or be quenched to below, the T_(g) whilemaintained in the desired deformed shape to “lock” in the deformation.Once the deformation is locked in, the polymer network cannot return toa relaxed state due to thermal barriers. The SMP will hold its deformedshape indefinitely until it is heated above its T_(g), whereat the SMPstored mechanical strain is released and the SMP returns to itsperformed state.

SMPs are not simply elastomers, nor simply plastics. They exhibitcharacteristics of both materials, depending on their temperature. Whilerigid, an SMP demonstrates the strength-to-weight ratio of a rigidpolymer; however, normal rigid polymers under thermal stimulus simplyflow or melt into a random new shape, and they have no “memorized” shapeto which they can return. While heated and pliable, an SMP has theflexibility of a high-quality, dynamic elastomer, tolerating up to 400%elongation or more; however, unlike normal elastomers, an SMP can bereshaped or returned quickly to its memorized shape and subsequentlycooled into a rigid plastic.

Several known polymer types exhibit shape memory properties. Probablythe best known and best researched polymer types exhibiting shape memorypolymer properties are polyurethane polymers. Gordon, Proc of FirstIntl. Conf. Shape Memory and Superelastic Tech., 115-120 (1994) andTobushi et al., Proc of First Intl. Conf. Shape Memory and SuperelasticTech., 109-114 (1994) exemplify studies directed to properties andapplication of shape memory polyurethanes. Another polymeric systembased on crosslinking polyethylene homopolymer was reported by S. Ota,Radiat. Phys. Chem. 18, 81 (1981). A styrene-butadiene thermoplasticcopolymer system was also described by Japan Kokai, JP 63-179955 toexhibit shape memory properties. Polyisoprene was also claimed toexhibit shape memory properties in Japan Kokai JP 62-192440. Anotherknown polymeric system, disclosed by Kagami et al., Macromol. RapidCommunication, 17, 539-543 (1996), is the class of copolymers of stearylacrylate and acrylic acid or methyl acrylate. Other SMP polymers knownin the art include articles formed of norbornene ordimethaneoctahydronapthalene homopolymers or copolymers, set forth inU.S. Pat. No. 4,831,094. Additionally, styrene copolymer based SMPs aredisclosed in U.S. Pat. No. 6,759,481 which is incorporated herein byreference.

Modern aircraft are perhaps one of the largest users of compositematerials. Composites are widely used in the aerospace industry toprovide aircraft components such as fuselages, wings and tail fins,doors and so on. This is because composite components have the physicalattribute of being relatively lightweight while at the same time havinghigh structural strength in comparison to metals. Such compositecomponents typically are of a sandwich construction. When damage occursto such structures, for example by impacted damage from a flying stoneor other debris or from a dropped tool, a damage crater, crack, or holewill be formed in the object concerned.

The general approach to repair damage is to remove the damaged part fromthe aircraft, and repair the damage by using an electric blanket with avacuum bag. A “prepreg” formed of a layer of fibrous materialimpregnated with uncured resin is laid over the area to be repaired. Theelectric blanket applies heat to that area to cure the prepreg. Thevacuum bag holds the electric blanket in position over the repair areawhile at the same time applying a compaction force to the prepreg.

Repairs using this approach are not however always satisfactory. This isbecause the inconsistency of the heat provided by the electric blanketleads to unreliability in the curing. Also, the use of vacuum bagcompaction is not very effective in removing air from the prepreg sothat the repaired area is not necessarily void free. Additionally, itnormally takes a long amount of time to remove, repair, replace, andtest the damaged component on an aircraft. Finally, the majority of timein using these methods typically involves waiting for the resin in thecomposite material and filler to cure. If this cure cycle was eliminatednot only would there be a vast reduction in time but also in theemissions and use of chemicals, eliminating the cleanup and disposal ofsaid chemicals.

A similar method of repair to such composite structures generallyentails a lightweight composite filler material being inserted into thecrater in a thixotropic state to protrude slightly from the outersurface. The filler is then allowed to harden and cure. It is thenabraided flush with the surface of the structure. A patch of fiberreinforced composite material in either cured or more generally uncuredstate is then adhered to the surface of the structure over the filledcrater using a separate adhesive and the patch is then bonded inposition using both vacuum and heat. The vacuum is normally appliedusing an airtight sheet of material placed over the repair andtemporarily sealed to the structure using a bead of adhesive around itsperiphery. A vacuum is then created under the sheet to try to ensurethat any air bubbles are expelled from underneath the patch and toensure good bonding. At the same time a heater blanket positioned insideor outside of the vacuum bag will apply heat to the repair to effecthardening and curing of the adhesive which is normally a curable resin.

Multi-layered repair patches are also known in the art and these repairpatches have been used both for repairing holes in drywall material aswell as repairing holes in automobile bodies. U.S. Pat. Nos. 5,075,149issued to Owens et al. (“Owens”), 4,707,391 issued to Hoffmann(“Hoffmann '391”) and 4,135,017 issued to Hoffmann (“Hoffmann '017”) areall directed to multi-layer repair patches.

Owens discloses a three-layered patch with a metal plate disclosedbetween two polyester sheets. The metal plate is held in place betweenthe two polyester sheets with a semi-solid adhesive such as urethane.The semi-solid adhesive fixedly attaches the two polyester sheetstogether as well as fixedly attaching the reinforcing metal platebetween the two sheets. Owens is not useful for repairs which requirethe application of bonding material or plaster to the repair patchbecause the bonding material or plaster cannot readily pass through themesh due to the presence of the urethane adhesive. Additionally, thepatch cannot be molded quickly, on-site, without additional time andequipment.

Hoffmann '391 discloses a two-layer patch including a perforated metalplate with an outer fiberglass mesh attached to one side of the plate. Aglue or adhesive coating is applied to the surface of the plate that isattached to the surface to be repaired and an additional adhesivecoating is applied to the inward-facing surface of the fiberglass meshto attach the mesh to the metal plate as well as to attach the mesh tothe surface under repair.

Hoffmann '017 also discloses a two-layer patch. An inner metal plate iscovered with adhesive that secures one surface of the plate to thesurface under repair. An outer plate cover is laminated onto theexterior side of the metal plate by means of a layer of adhesive appliedto the inward-facing side of the plate cover.

Both of these methods employ metal plates in the final patch with limitsthe ability of these patches to be easily and quickly molded to thedamaged part on-site. Additionally, the use of metal eliminates some ofthe weight saving advantages of a pure composite repair patch.

Additionally, the repairs alone in these methods can take approximatelyfour hours or more to complete, mainly due to the time necessary toallow curing of the filler and adhesive. When taking into account thetime to remove the damaged parts, mold the patch to the damaged area,and replace the part, the time involved increases. In addition, despitethe use of vacuum equipment to attempt to expel all air entrapped underthe patch, the complete absence of such entrapment cannot be guaranteedand non-destructive testing may need to be carried out to ensure thestructural integrity of the repair. With aircraft downtime often runningat $US100,000.00 per hour it will be appreciated that enormous potentialsavings are possible when employing the method of the instant invention.

Additionally, if mass produced items, such as car hoods, bumpers, andother manufactured parts are damaged, it is oftentimes less expensive toreplace the entire part than to repair it, although such parts are oftenexpensive themselves. Thus there is a need for a cheap, quick, andeffective method of repairing such mass produced parts and for quicklyand reliably repairing aircraft and other high end parts.

2. Epoxy Background

Shape memory materials are materials capable of distortion above theirglass transition temperatures (T_(g)s), storing such distortion attemperatures below their T_(g) as potential mechanical energy in thematerial, and release this energy when heated again to above the T_(g),returning to their original “memory” shape.

The first materials known to have these properties were shape memorymetal alloys (SMAs), including TiNi (Nitinol), CuZnAl, and FeNiAlalloys. These materials have been proposed for various uses, includingvascular stents, medical guide wires, orthodontic wires, vibrationdampers, pipe couplings, electrical connectors, thermostats, actuators,eyeglass frames, and brassiere underwires. With a temperature change ofas little as 10° C., these alloys can exert a stress as large as 415 MPawhen applied against a resistance to changing its shape from itsdeformed shape. However, these materials have not yet been widely used,in part because they are relatively expensive.

Shape memory polymers (SMPs) are being developed to replace or augmentthe use of SMAs, in part because the polymers are light weight, high inshape recovery ability, easy to manipulate, and economical as comparedwith SMAs. SMPs are materials capable of distortion above their glasstransition temperature (T_(g)), storing such distortion at temperaturesbelow their T_(g) as potential mechanical energy in the polymer, andrelease this energy when heated to temperatures above their T_(g),returning to their original memory shape. When the polymer is heated tonear its transition state it becomes soft and malleable and can bedeformed under resistances of approximately 1 MPa modulus. When thetemperature is decreased below its T_(g), the deformed shape is fixed bythe higher rigidity of the material at a lower temperature while, at thesame time, the mechanical energy expended on the material duringdeformation will be stored. Thus, favorable properties for SMPs willclosely link to the network architecture and to the sharpness of thetransition separating the rigid and rubbery states.

Heretofore, numerous polymers have been found to have particularlyattractive shape memory effects, most notably the polyurethanes,polynorbornene, styrene-butadiene copolymers, and cross-linkedpolyethylene.

In literature, SMPs are generally characterized as phase segregatedlinear block co-polymers having a hard segment and a soft segment, seefor example, U.S. Pat. No. 6,720,402 issued to Langer and Lendlein onApr. 13, 2004. As described in Langer, the hard segment is typicallycrystalline, with a defined melting point, and the soft segment istypically amorphous, with a defined glass transition temperature. Insome embodiments, however, the hard segment is amorphous and has a glasstransition temperature rather than a melting point. In otherembodiments, the soft segment is crystalline and has a melting pointrather than a glass transition temperature. The melting point or glasstransition temperature of the soft segment is substantially less thanthe melting point or glass transition temperature of the hard segment.Examples of polymers used to prepare hard and soft segments of knownSMPs include various polyacrylates, polyamides, polysiloxanes,polyurethanes, polyethers, polyether amides, polyurethane/ureas,polyether esters, and urethane/butadiene copolymers.

The limitations with these are other existing shape memory polymers liein the thermal characteristics and tolerances of the material. The T_(g)of a material may be too low for the conditions in which the system willreside, leading to the material being incapable of activation. Anexample of such a situation is an environment with an ambienttemperature exceeding the transition temperature of the SMP; such aclimate would not allow the polymer to efficiently make use of its rigidphase. Additionally, current organic systems from which SMPs aresynthesized are not capable of operating in adverse environments thatdegrade polymeric materials. An example of such an environment is lowearth orbit, where intense radiation and highly reactive atomic oxygendestroy most organic materials.

Applications for a shape memory material capable of withstanding theseharsh conditions as well as higher thermal loads include, but are notlimited to; morphing aerospace structures and space compatible polymerscapable of self-actuation and dampening.

As discussed in Langer, SMP can be reshaped and reformed multiple timeswithout losing its mechanical or chemical properties. When the SMPdescribed by Langer is heated above the melting point or glasstransition temperature of the hard segment, the material can be shaped.This (original) shape can be memorized by cooling the SMP below themelting point or glass transition temperature of the hard segment. Whenthe shaped SMP is cooled below the melting point or glass transitiontemperature of the soft segment while the shape is deformed, a new(temporary) shape is fixed. The original shape is recovered by heatingthe material above the melting point or glass transition temperature ofthe soft segment but below the melting point or glass transitiontemperature of the hard segment. The recovery of the original shape,which is induced by an increase in temperature, is called the thermalshape memory effect. Properties that describe the shape memorycapabilities of a material are the shape recovery of the original shapeand the shape fixity of the temporary shape.

Conventional shape memory polymers generally are segmented polyurethanesand have hard segments that include aromatic moieties. U.S. Pat. No.5,145,935 to Hayashi, for example, discloses a shape memory polyurethaneelastomer molded article formed from a polyurethane elastomerpolymerized from of a difunctional diisocyanate, a difunctional polyol,and a difunctional chain extender.

Examples of additional polymers used to prepare hard and soft segmentsof known SMPs include various polyethers, polyacrylates, polyamides,polysiloxanes, polyurethanes, polyether amides, polyurethane/ureas,polyether esters, and urethane/butadiene copolymers. See, for example,U.S. Pat. No. 5,506,300 to Ward et al.; U.S. Pat. No. 5,145,935 toHayashi; and U.S. Pat. No. 5,665,822 to Bitler et al.

Several physical properties of SMPs other than the ability to memorizeshape are significantly altered in response to external changes intemperature and stress, particularly at the melting point or glasstransition temperature of the soft segment. These properties include theelastic modulus, hardness, flexibility, vapor permeability, damping,index of refraction, and dielectric constant. The elastic modulus (theratio of the stress in a body to the corresponding strain) of an SMP canchange by a factor of up to 200 when heated above the melting point orglass transition temperature of the soft segment. Also, the hardness ofthe material changes dramatically when the soft segment is at or aboveits melting point or glass transition temperature. When the material isheated to a temperature above the melting point or glass transitiontemperature of the soft segment, the damping ability can be up to fivetimes higher than a conventional rubber product. The material canreadily recover to its original molded shape following numerous thermalcycles, and can be heated above the melting point of the hard segmentand reshaped and cooled to fix a new original shape.

Recently, SMPs have been created using reactions of different polymersto eliminate the need for a hard and soft segment, creating instead, asingle piece of SMP. The advantages of a polymer consisting of a singlecrosslinked network, instead of multiple networks are obvious to thoseof skill in the art. The presently disclosed invention uses this newmethod of creating SMPs. U.S. Pat. No. 6,759,481 discloses such a SMPusing a reaction of styrene, a vinyl compound, a multifunctionalcrosslinking agent and an initiator to create a styrene based SMP.

The industrial use of SMPs has been limited because of their lowtransition temperatures. Epoxy resins are a unique class of materialwhich possesses attractive thermal and mechanical properties. Epoxyresins polymerize thermally producing a highly dense crosslinkednetwork. Typically these thermoset epoxy networks are rigid and have lowstrain capability. By altering this network system, it is possible toproduce a lightly crosslinked network still possessing many of theoriginal materials properties but with the functionality of a shapememory polymer. Currently there is no epoxy based SMP available.

High temperature, high toughness thermoset resins with shape memorycharacteristics are not currently available. Other high temperature,high toughness, thermoset resins do not have shape memory. Typically,epoxy resins do not exhibit the shape memory effect mentioned above. Inorder to exhibit this shape memory effect epoxy resins must becrosslinked in a manner different from normal epoxy resins. It is thisnew method of crosslinking epoxy resins that is highly sought after.

It is the object of the present invention to provide a preformed andcured patch and a method to quickly and cheaply permanently repair anynumber of items with composite materials which retain similar or greatermechanical properties of the parts repaired. Another object is toprovide a method for quickly and cheaply joining two parts together inorder to form a larger part which retains similar mechanical propertiesof the original parts. These and other objects of the present inventionwill become apparent from the following specification.

SUMMARY OF THE INVENTION

According to a first aspect of the invention there is provided a patchof fiber reinforced shape memory polymer resin composite material forattachment to a surface of a fiber reinforced plastics composite, metal,wood, or plastic structure over an area of damage to the structure, thepatch defining an outer surface, a bonding surface opposed thereto and aperipheral edge, the patch including fiber reinforcement and shapememory polymer resin as the matrix material with said matrix materialbeing in a substantially final state of hardness. The patch mayconveniently include a final protective coating applied to the outersurface thereof. The process according to the first aspect is primarilyto be used for temporary or cosmetic repair of manufactured parts.

This patch and process reduces the time to repair composite parts andother material and eliminates the creation of volatile components thatmust not be released into the environment as per EPA requirements duringthe repair process. The combination of both of these factors makes thisprocess highly transferable into mass production of patches forhigh-performance composites at an affordable price and for the massproduction of patches for use in lower performance items as well.Additionally the patch can be molded on site by hand, without the use ofsignificant amounts of equipment or special orders to pre-mold thecomposite patch to match the specific damaged area. Another benefit isthat by using shape memory polymer as the resin the damaged part doesnot need to be removed from the larger component, for example removingthe wing from the airplane, in order to mold the patch and repair thedamage.

The patch, according to the first aspect of the invention, willtypically be in some predetermined memorized geometric shape, typicallya flat square or rectangle, but can be in any desired preformed shape.In order to mold the patch to the desired shape, the shape memorypolymer resin is activated, typically using heat to raise thetemperature of the shape memory polymer resin above its activationtemperature or light to activate the shape memory polymer, at whichpoint the shape memory polymer resin, and the entire composite part,become soft and can be mechanically deformed, typically by hand, to thedesired shape. Once the composite part has cooled below the activationtemperature of the shape memory polymer resin or has been deactivated bylight, the composite part will retain the new, deformed shape, and canbe bonded to the damaged part with adhesives.

Bonding the patch to the damaged part is typically accomplished withsome form of adhesive. While some adhesives may require heat curing,choosing the correct shape memory polymer to use as the resin matrixwill prevent this curing from causing the composite material to becomesoft again, and lose its molded shape, especially if using a lightactivated shape memory polymer resin. This presents little difficulty ascuring the adhesive may include raising the temperature thereof to atemperature less than substantially 100° C. where there is a largeavailability of shape memory polymers whose activation temperatures areabove 100° C. It will be appreciated that adhesive cure temperaturescould be as high as 180° C., but repairs in the field are likely to bemore sound if a lower curing temperature resin is used to avoid thepossibility damage to the composite patch or further damage to the partbeing repaired. Additionally, certain formulations and types of shapememory polymer can be made with a transition temperature well in excessof 180° C. such that high cure temperatures for most adhesives are oflittle concern. Where the adhesive is a curable resin the method mayinclude the step of curing the adhesive for a period less than one hour.Such a short curing time can dramatically shorten the overall repairtime according to the method of the invention, especially when only theadhesive and not the resin in the patch requires curing. Furthermore,some adhesives, such as pressure sensitive adhesives, require no curing,thus eliminating this concern.

Manufacture of the patch according to the invention includes creating acured composite patch within a shape memory polymer resin matrix. Thepatch is preformed to a predetermined, memorized shape. The compositepatch may be of any required thickness and any suitable number of layersof fibrous material within a shape memory polymer resin matrix, one ormore, in order to give the required structural strength in particularcircumstances.

It will be appreciated that when carrying out the repair method of theinvention all the normal preparatory work may be done to the damagedarea in the usual way, for example thorough drying thereof, abrasion andcleaning of the surface to be repaired and debris and sharp edgeremoval. Best results for the repair are likely to be obtained when theliquid adhesive is painted onto all contact areas with a brush or thelike to ensure good adhesion.

The method of the invention thus enables the use of the patch accordingto the first aspect of the invention in a manner which avoids the use ofa separate filler material which must be separately hardened and abradedflush with the surface to be repaired prior to the application of thepatch thereto with, again, a separate adhesive. Additionally, the methodof the inventions enables use of a patch without any curing of the resinemployed in the composite patch. Overall time savings for repairsaccording to the method of the invention are expected to be at leastthree hours over prior art methods.

A second aspect of the invention allows for the permanent repair ofmanufactured parts including high strength applications of airplaneparts and boat hulls. According to the second aspect of the inventionthere is provided a patch of fiber reinforced shape memory polymer resincomposite material for attachment to a surface of a fiber reinforcedplastics composite, metal, wood, or plastic structure over an area ofdamage to the structure, the patch defining an outer surface, a bondingsurface opposed thereto and a peripheral edge, the patch including fiberreinforcement and shape memory polymer resin as the matrix material withsaid matrix material being in a substantially final state of hardness.The patch may conveniently include a final protective coating applied tothe outer surface thereof.

A second aspect of the invention allows for the quick and easy permanentrepair of composite parts or other material. According to the secondaspect a part has been damaged and requires permanent repair. Typicallythe damaged section will have damage to the composite part andpotentially damage to the underlying layers. Since the majority of timein repairing composite parts and other manufactured components withcomposite patches involves the curing of the composite eliminating thisstep will significantly reduce the amount of time and effort spent inrepair. It is to be appreciated that the initial steps of creating aseamless transition phase between the damaged and undamaged sections ofthe part can be accomplished by normal means. Additionally, repair tothe underlying filler, foam, or other material can be accomplished in anormal means.

Once the damaged area has been removed and a transition area has beencreated, smoothed, machined, cleaned, and otherwise prepared for repair,a preformed composite patch within a shape memory polymer resin matrixcan be used. After activating the patch's shape memory polymer witheither heat or light (or other electromagnetic radiation), the patch isthen formed and molded into the damaged area either manually or withother means of assistance. Once the composite patch has been molded tothe damaged area deactivate the shape memory polymer by letting it coolbelow its transition temperature or exposing it to light or otherelectromagnetic radiation. When the patch is hard, simply bond thecomposite material to the damaged part, clean and machine the patch toremove any excess patch material to ensure it is flush and level withthe damaged part, and sand, finish, and coat if necessary with standardmethods.

This patch and process reduces the time of composite repair andeliminates the creation of VOC (volatile components that must be not bereleased into the environment as per EPA requirements) during the repairprocess. The combination of both of these factors makes this processhighly transferable into mass production of high-performance compositesat an affordable price. Additionally, it is to be appreciated that thismethod of repair requires no curing time for the composite patch andeliminates the need to wait for any layer to cure before proceeding withthe repair, thus significantly reducing the time to permanently repair adamaged part.

Another aspect of the invention allows the joining of two parts tocreate a single, larger part without the use of expensive welding,molding, or other methods that use expensive chemicals or require othercontrols to prevent discharge of chemicals and vapors. By placing two ormore parts of similar or dissimilar shape or size in juxtaposition andusing the patch to connect the parts, a larger part can be created. Oncethe patch is soft from activation of the shape memory polymer resin iscan be molded to ensure a tight connection between two parts, even ifthe parts are of significant geometries. Once bonded to the individualparts, the larger part can be used.

Another embodiment is the repairing of material with a piece of shapememory polymer. This method is best used in processes where highstrength is less preferable to other desires. This is accomplished in amanner similar to the composite patch.

Additional embodiments of the present invention include the use of othermeans of molding the composite patch and bonding said patch to thedamaged part.

The epoxy based shape memory polymers (SMPs) that are described in thisapplication are well adapted for industrial use in making SMP Molds, asset forth in U.S. Pat. No. 6,986,855 issued to Hood and Havens on Jan.17, 2006, or for use in other industrial and manufacturing processes.

As previously stated, SMPs are a unique class of polymers that canharden and soften quickly and repetitively on demand. This featureprovides the ability to soften temporarily, change shape, and harden toa solid structural shape in various new highly detailed shapes andforms.

SMPs have a very narrow temperature span in which they transition fromhard to soft and back again. Additionally it is possible to manufacturethe SMP such that the activation of the SMP occurs over a very narrowtemperature range, typically less than 5 degrees Celsius. This narrowglass transition temperature (T_(g)) range is a key property that allowsa SMP to maintain full structural rigidity up to the specificallydesigned activation temperature. SMPs possessing these properties, suchas described here, are particularly useful in applications that willchange shape at some stage but need the structure to stay rigid athigher operating temperatures, typically greater than 0° C., such asmorphing aerospace structures and SMP molding processes.

In accordance with the present invention, the SMPs disclosed are areaction product of at least one reagent containing two activeamino-hydrogen or two active phenolic-hydrogen with at least onemultifunctional cross linking reagent which contains at least three ormore active amino- or phenolic-hydrogen or is a reagent containing atleast three glycidyl ether moieties which is then further mixed with atleast one diglycidyl ether reagent whereupon the resulting mixture iscured and has a glass transition temperature higher than 0° C. Thisreaction creates crosslinking between the monomers and polymers suchthat during polymerization they form a crosslinked thermoset network.

Therefore it is an object of the present disclosure to provide anepoxy-based polymer containing a crosslinked thermoset network whichexhibits the shape memory effect described above which is useful inmaking the shape memory polymer patches.

Other objects, features and advantages of the invention will be apparentfrom the following detailed description taken in connection with theexamples and accompanying drawings and are within the scope of thepresent invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a typical pipe with a damaged area.

FIG. 2 is a perspective view of a shape memory polymer composite patch.

FIG. 3 is a perspective view of a typical pipe with damage repaired bythe shape memory polymer composite patch.

FIG. 4 is a perspective view of a typical pipe with damage at or near awall, floor, or ceiling.

FIG. 5 is a perspective view of a typical pipe with damage at or near awall, floor, or ceiling repaired by the shape memory polymer compositepatch.

FIG. 6 is a perspective view of two short pieces of pipes that are to bejoined together.

FIG. 7 is a perspective view of the single long pipe created from thetwo shorter pipes joined by the shape memory polymer composite patch.

FIG. 8 is a perspective view of two flat pieces that are to be joinedtogether.

FIG. 9 is a perspective view of a single piece created from the twosmaller pieces joined by two sheets of shape memory polymer compositepatch.

FIG. 10 is a perspective view of a section of a boat that has a damagedarea.

FIG. 11 is a sectional view of the same damaged area showing thefiberglass coating and damaged area.

FIG. 12 is a perspective view of the shape memory polymer compositepatch with slightly angled sides for a better fit of the patch.

FIG. 13 is a sectional view of the damaged area after the damage areahas been removed and a transition area from undamaged to damaged areahas been created.

FIG. 14 is a sectional view of the of the damaged area ready for repairand the soft composite patch that is ready for molding into the damagedarea.

FIG. 15 is a sectional view of the of the boat hull with the compositepatch essentially repairing the damaged area with some excess patchmaterial extending beyond the original hull.

FIG. 16 is a sectional view of the machined and sanded patch so that thepatch and the original hull are flush.

FIG. 17 is a perspective view of the hull fully repaired by the shapememory polymer composite patch.

DETAILED DESCRIPTION OF THE INVENTION SMP Patch

Referring to the drawings in greater detail, the method of the inventionherein is directed to fabricating and using a composite patch with aShape Memory Polymer (SMP) resin matrix or other shape memory materialin the manufacture of castable composite parts.

Examples 1 and 2 below describe the exemplary methods of creatingpre-form shape memory polymer (SMP) composite parts. In general, thepreferred SMP is a styrene copolymer based SMP as disclosed in U.S. Pat.No. 6,759,481, however, other types of SMPs such as cyanate ester,polyurethane, polyethylene homopolymer, styrene-butadiene, polyisoprene,copolymers of stearyl acrylate and acrylic acid or methyl acrylate,norbornene or dimethaneoctahydronapthalene homopolymers or copolymers,malemide and other materials are within the scope of the presentinvention.

Example 1

A polymeric reaction mixture was formulated by mixing vinyl neodecanoate(10%), divinyl benzene (0.8%), and styrene (85.2%) in random order toyield a clear solution. Benzoyl peroxide paste (4%) which is 50% benzoylperoxide, was then added to the resulting solution (all composition %are by weight). The resulting solution was kept cold in a refrigeratorbefore use. To prepare the shape memory polymer resin matrix compositesheet, a piece of 3D weave carbon fiber is placed on a glass sheet,ensuring that there are no stray fibers and the carbon fiber piece issmooth. Next, pour some of the polymeric reaction mixture onto thecarbon fiber. Use a plastic squeegee or plastic spreader to spread theresin evenly over the entire surface of the fabric. Thoroughly removeair bubbles and straighten the fabric. Place bleeder and breather fabricon top of the resin soaked carbon fiber. Then place the entire system ina high temperature vacuum bag with a vacuum valve stem and apply vacuumthoroughly, ensuring that there are no leaks. Cure the composite partwith the following cycle: 1) A one-hour linear ramp to 75° C. in anoven, autoclave, or other form of controlled heating device; 2) Athree-hour hold at 75° C.; 3) A three-hour linear ramp to 90° C.; 4) Atwo-hour linear ramp to 110° C.; 5) A one-hour linear ramp to 20° C.After curing, remove from oven and allow to cool. Remove vacuum bag,bleeder fabric, breather fabric, and glass plates from composite.

Example 2

A polymeric reaction mixture was formulated by mixing vinyl neodecanoate(10%), divinyl benzene (0.8%), and styrene (55.2%) in random order toform a colorless solution. Polystyrene granules (30%) were then added tothe resulting solution. The resulting mixture was then allowed to sit atroom temperature with occasional stirring until all the polystyrenegranules were dissolved to give a clear, viscous solution. Benzoylperoxide (4%) which is 50% benzoyl peroxide was then added to theresulting solution (all composition % are by weight). The resultingpolymeric reaction mixture is continually stirred at or near 25° C., notto exceed 30° C. until a clear solution is achieved which can take 2hours or more. The resulting solution is kept cold in a refrigeratorbefore use. To prepare the shape memory polymer resin matrix compositesheet, a piece of 3D weave carbon fiber is placed on a glass sheet,ensuring that there are no stray fibers and the carbon fiber piece issmooth. Next, pour some of the polymeric reaction mixture onto thecarbon fiber. Use a plastic squeegee or plastic spreader to spread theresin evenly over the entire surface of the fabric. Thoroughly removeair bubbles and straighten the fabric. Place bleeder and breather fabricon top of the resin soaked carbon fiber. Then place the entire system ina high temperature vacuum bag with a vacuum valve stem and apply vacuumthoroughly, ensuring that there are no leaks. Cure the composite partwith the following cycle: 1) A one-hour linear ramp to 75° C. in anoven, autoclave, or other form of controlled heating device; 2) Athree-hour hold at 75° C.; 3) A three-hour linear ramp to 90° C.; 4) Atwo-hour linear ramp to 110° C.; 5) A one hour linear ramp to 20° C.After curing, remove from oven and allow to cool. Remove vacuum bag,bleeder fabric, breather fabric, and glass plates from composite.

To achieve more than one fabric layer simply soak two or more layers offabric in the shape memory polymer and stack on top of each other. Theuse of other fabrics such as carbon nano-fibers, spandex, chopped fiber,random fiber mat, fabric of any material, continuous fiber, fiberglass,or other type of textile fabric can be used to replace carbon fiber inthe above examples. In Example 2 it is essential that while mixing afterthe addition of benzyl peroxide that the temperature of the resin bemaintained below 30° C. as the mixture may become hot and explosive.Mixing in a cold water or ice bath ensures the temperature will notexceed 30° C. It can take two hours or more to fully mix.

Additionally, once cured, the shape memory polymer composite can bedeformed for easy storage, shipping, or immediate use. If deformed forstorage or shipping, simply activating the shape memory polymer resinwill restore the composite part to its original, memorized shape.

The method of repairing all types of components and the composite patchjoining system all utilize the same common features. The followingdescription therefore relates to all of these features.

FIG. 1 shows a typical pipe, 2, with a crack, 4. FIG. 2 shows a flat,essentially square piece of shape memory polymer resin composite, 6.After activation, the shape memory polymer resin in 6 will become softand can be easily molded to a variety of shapes. In the present example,a technician, wearing gloves, can easily mechanically deform 6 to coverthe crack 4 and follow the curvature of the pipe 2 as seen in FIG. 3where the deformed patch, 8, covers the crack and essentially replicatesthe shape of the pipe. After bonding the patch to the pipe with anadhesive the pipe is repaired and can continue with normal operations.

This process of patching various holes, cracks, leaks, and other damagesis not limited to simple shapes. FIG. 4 shows a larger hole, 12, at thejoint between a pipe, 10, and the ground, wall, or ceiling. Again, afteractivation, the shape memory polymer resin in 6 will become

Additionally these repairs can be conducted not only by compositematerial but also by pure shape memory polymer resins which undergo thesame activation, deformation, and bonding as seen in the abovedescription.

Another embodiment of the invention is the ability to join two or moreparts together easily in order to form larger parts. FIG. 6 shows twoshort pipes, 16 and 18. If it is desired to create a larger pipe fromthese two it may be very difficult or time consuming to weld orotherwise join these pipes. Using a composite patch or patch of shapememory material a single pipe can easily be made out of 16 and 18 asshown in FIG. 7. After placing 16 and 18 end to end in order to form asingle pipe, the shape memory polymer resin composite or pure shapememory polymer patch is activated and deformed around the pipe in orderto effect a joining of the pipes with the deformed patch, 20. Afterbonding the patch to the pipes a new long pipe, 22, is created. Thisentire process can be quick and reduces the emission and use oftypically bonding or welding tools that create fire and chemical hazardsupon use.

This embodiment is not limited to pipes and can be used to join othergeometric shapes together. FIG. 8 shows flat panels, 24 and 26, that mayjoined. FIG. 9 shows that with the use of two patches, 28 and 30, theflat panels can quickly be joined without deforming the patches ordeforming the panels so that patches can match the minor changes in theshape of the boards. After bonding the patches to the panels, a newlarger panel, 32, is created.

Another exemplary embodiment provides a means of permanent repair formanufactured parts that can significantly reduce the time required forrepair. In FIG. 10 there is shown a section of a boat hull that hassuffered damage, 38. The boat hull is made of a fiberglass outer layer,36, and a filler or foam inner layer, 34. FIG. 11 shows a sectional viewof the damaged hull, 38, with the outer fiberglass layer, 36, damagedfrom a piece of debris. While no damage is shown to the filler or foaminner layer, 34, if such damage present, this damage could be repairedwith normal methods. FIG. 12 shows a composite patch material, 40, madeby the process of Example 1 above except that fiberglass, instead ofcarbon fiber, is used as the fibrous material. In order to repair thedamaged area, 38, shown in FIGS. 10 and 11, the damaged area must beremoved, as shown at 42 in FIG. 13, and a clean, smooth transition areais created, shown as 43. As shown in FIG. 13 the boat hull has beenmachined to create transition regions, 43, on all sides of the damagedarea from undamaged fiberglass composite structure to the area to berepaired, 42.

Once the surface has been prepared for repair using normal methods, theshape memory polymer composite patch, 40, is activated by raising itstemperature above its T_(g). As shown in FIG. 14 the composite patch isthen initially deformed, 44, into a shape that will make it easier tomold into the damaged area, 42, and the transition area, 43. While thetemperature of the composite patch is above its T_(g), the compositepatch is formed and molded into the damaged area, 42, and surrounded bythe transition area, 43, so that the entire damaged area and transitionarea are essentially covered by the patch. As shown in FIG. 15 the nowmolded composite patch, 46, has been placed so as to essentially coverthe entire damaged area. Additionally, the molded patch, because of itssoft and pliable state while heated, is able to fill in most gaps andcrevices and completely replicate the entire damaged area and machinedtransition area. As previously noted, this process requires no cure timeas the composite patch is already in an essentially cured state. Oncethe patch has been molded to the desired area, simply allow the patch tocool below its T_(g) to return the patch to a hard, rigid state. Thisprocess should only take a few minutes.

The composite patch can be bonded to the original part with a variety ofsystems discussed below. Once cooled and bonded to the original part itis possible that there will be some excess material that will rise aboveand/or not be flush with the original, undamaged surface, as shown at 47in FIG. 15. This excess material can be removed through sanding or othermachine processes as shown in FIG. 16 where the final surface, 48, ofthe composite patch, 46, is now flush with the original part. FIG. 17shows a final view of the patch, 50, used to fully repair the damagedarea, 38, in FIG. 10. The composite patch is now flush with the surfaceand may be coated or painted as desired. It is to be appreciated thatthese repairs can be conducted not only by composite material but alsoby pure shape memory polymer resins which undergo the same activation,deformation, and bonding as seen in the above descriptions. It is alsoto be appreciated that this method of permanent repair can also be usedfor airplane parts, car parts, and any other manufactured part that canbe repaired using composite material.

In order to bond the composite patch to a variety of systems, theadhesive must be chosen very carefully. There are a variety ofcommercially-available adhesive systems for use in bonding shape memorypolymer composite patches to different substrates. The wide range ofadhesives will aid in developing different patch systems for differentapplications. Some adhesives are aerospace compatible, while others canonly be used for ground applications or mass produced items. Cryogeniccompatible adhesives are also available for use in repairing cryogenicpipes and tanks. These adhesives can be divided into two categories:thermally cured adhesives and pressure sensitive adhesives. Thethermally cured adhesives chosen can be cured at or above the transitiontemperature of the shape memory polymer composite as pressure and heatare applied to cure the adhesive, and the patch is soft and easilyformed around the area to be patched. The pressure sensitive adhesivesare effective for quick repairs in sealing spaces that contain differentenvironments such as the inside of pressure vessels and gas or liquidconduits. These adhesives allow for a quick “bandage-type” approachuntil a more permanent solution could be achieved. The followingadhesives could be used for various applications, but is not intended tolimit adhesives within the scope of the present invention to only thoselisted below:

Thermally Cured Adhesives

LORD Corporation Products

-   -   310 A/B Epoxy Adhesive    -   7542 A/E Urethane Adhesive

3M Products

-   -   Scotch-Weld AF 563K Film Adhesive    -   Scotch-Weld AF 163-2 Film Adhesive    -   Scotch-Weld EC 3333 B/A 2-Part Paste Adhesive    -   Scotch-Weld EC 3448 Paste Adhesive (1-Part)

Loctite Products

-   -   Hysol® EA 9309.3 NA Epoxy Paste Adhesive    -   Hysol® 615    -   Hysol® U-05FL    -   Hysol® EA 9361 Epoxy Paste Adhesive    -   Hysol® EA 9628 Epoxy Film Adhesive    -   Hysol® EA 9695 Epoxy Film Adhesive    -   Hysol® EA 9696 Epoxy Film Adhesive

Pressure Sensitive

3M Products

-   -   9244 Structural Bonding Tape    -   468 MPR Structural Bonding Tape    -   9485 PC High-Performance Adhesive Transfer Tape

Budnick Converting, Inc. Products

-   -   P02—Multi-purpose Double-Coated Splicing & Mounting    -   1198—UHA Adhesive Transfer    -   P50—Multi-purpose Double-Coated Cloth Tape

The thermally cured adhesives can be applied by: 1) forming the shapememory polymer composite patch around the area to be bonded (withoutadhesive); 2) applying adhesive to the patch; and then 3) bonding thepreformed patch to the damaged area through thermal cure. This approachis the easiest and cleanest method for using paste-type adhesives. Thismethod may be enhanced by using vacuum pressure during thermal cure andchoosing an adhesive that has a cure temperature above the transitiontemperature of the shape memory polymer composite used for the patch.This would allow for a more intimate interface between the patch and thesubstrate during cure. This helps promote distributed load transferthrough the adhesive.

Pressure adhesives are applied to the shape memory polymer compositepatch manually with the backing paper left intact. When repair isdesired, 1) the patch/adhesive combination is heated above thetransition temperature of the composite patch, 2) the backing paper isremoved and 3) the patch is formed manually or with assistance andadhered simultaneously to the substrate. This method of adhesiveapplication prior to use enables very fast repair scenarios.Additionally for light or electromagnetic radiation activated shapememory polymer composites, the patch adhesive combination is activatedby application of said electromagnetic radiation, the patch is formedmanually or with other mechanical assistance to the substrate anddeactivated with electromagnetic radiation.

The following are examples of the process of bonding shape memorypolymer composites to substrates according to all aspects of theinvention:

Example 3

In order to bond a shape memory polymer composite patch to fiberglass,the area around the damaged portion of a part or the area near theportion of the part to be joined to another, the applicable area isscuff sanded and solvent wiped to ensure a clean, smooth bondingsurface. Additionally, scuff sand and solvent wipe the side of the patchto be bonded to the substrate. Using 3M's 9485 PC High-PerformanceAdhesive Transfer Tape, apply the tape to the patch manually leaving thebacking on the adhesive. Using the patch from Example 1 heat the patchabove its transition temperature in an oven which is at or near 90° C.Remove the patch/adhesive from the oven, peel away the adhesive backingand form patch to fiberglass surface manually or with assistance of avacuum pad or bagging.

Example 4

In order to bond a shape memory polymer composite patch to stainlesssteel the area around the damaged portion of a part or the area near theportion of the part to be joined to another is scuff sanded and solventwiped to ensure a clean, smooth bonding surface. Additionally scuff sandand solvent wipe the side of the patch to be bonded to the substrate toensure a smooth bonding surface. Apply a thin, even layer of LoctiteHYSOL U05-FL paste adhesive to repair area on stainless steel. Using thepatch from Example 1 heat the patch above its transition temperature.Form patch to repair surface manually or with a heating blanket usingvacuum pressure. Cure adhesive according to manufacturersrecommendations using temperature controller connected to the heatingblanket or other method. Remove vacuum blanket after cure.

The bonding of the shape memory polymer composite patch can be done tovarious other substrates, metal cans, car fenders, other compositeparts, using the method of Example 3 above. The methods described aboveare useful and one method should be chosen over the other methoddepending on the application. Thermally cured adhesives should generallybe used for higher strength applications where time-to-repair is lesscritical such as airplane parts, load-bearing structural parts, andother parts with high strength or other mechanical properties asdescribed in Example 4 above. Pressure sensitive adhesives shouldgenerally be used for lower strength applications where time-to-repairis more critical or the cost or strength is not as important such asleaking pipes or simple cosmetic repairs. After bonding with the correctadhesive and composite patch, the repaired part may be used normally.This includes flowing liquids or gasses through pipes at normaloperating temperatures and pressures.

Because of the properties inherent in shape memory polymers, compositesutilizing shape memory polymer as the resin matrix can be temporarilysoftened, reshaped, and rapidly hardened in real-time to function in avariety of structural configurations. They can be fabricated with nearlyany type of fabric, and creative reinforcements can result in dramaticshape changes in functional structures and they are machinable.

Therefore, it can readily be seen that the present invention provides aquick and easy way to utilize composite and shape memory polymertechnology to create a patch that has the flexibility of duct tape withthe performance of composites and similar metal substances.

It is therefore apparent that one exemplary embodiment of the inventionprovides a method for repairing manufactured parts of the type having adamaged area thereof. A repair material is preformed into a desiredshape. The repair material may comprise, for example, a shape memorypolymer. The shape memory polymer is activated so that the preformedrepair material becomes soft, and it is then deformed into a shapeadapted for the repair function. The shape memory polymer is thendeactivated while maintaining the polymer in its deformed state.Thereafter, the deformed shape memory polymer is bonded to the damagedarea of the manufactured part.

The repair material may comprise a composite material formed from atleast one layer of fibrous material in combination with a shape memorypolymer. In one form, the fibrous material may be embedded within theshape memory polymer or, the fibrous material can be impregnated withthe shape memory polymer.

The fibrous material may be chosen from carbon nanofibers, carbon fiber,spandex, chopped fiber, random fiber mat, fabric of any material,continuous fiber, fiberglass, or other types of textile fibers, yarns,and fabrics. For example, the fibrous material may be present in theform of a flat woven article, a two-dimensional weave, or athree-dimensional weave.

The shape memory polymer may be selected from a host of polymer typesincluding styrene, cyanate esters, maleamide polymers, epoxy polymers,or vinyl ester polymers. In some cases, the shape memory polymer will bea thermoset resin.

The repair material may include a thermal energy generation meansembedded therein. Such thermal energy generation means may comprise, forexample, thermally conductive fibers or electrical conductors.

In another exemplary embodiment of the invention, activation of theshape memory polymer is achieved by heating the polymer above itstransition temperature. The heating may, for example, be effected byinductive heating, hot air, or by heat lamps. Additionally, when therepair material comprises a thermal energy generation means embeddedtherein, it may be activated by applying electrical current to thethermal energy generation means.

In yet another exemplary embodiment of the invention, activation of theshape memory polymer may be achieved by application of electromagneticradiation such as in the form of visible light or ultraviolet light.

The deformation step may be achieved via mechanical means such as bypressing in a press mold or by extruding the material through a rollingdie mold.

In one exemplary embodiment of the invention, the shape memory polymeris deactivated by reducing the temperature thereof to below itsactivation temperature. This can be accomplished while the polymer isbeing press molded so that during the press molding, the polymer ismaintained at a temperature below its activation temperature. Further,the deactivation of the shape memory polymer may be achieved byapplication of electromagnetic radiation such as visible light orultraviolet light thereto.

The manufactured part may be composed of any material, such as metal,wood, plastic, glass, or in itself may be a composite part or similarmaterial. The bonding step in accordance with the invention may beachieved via a host of conventional means such as via thermally curedadhesives or pressure sensitive adhesives.

In addition to shape memory polymers, other shape memory materials suchas shape memory alloys may be mentioned as being effective.

Another aspect of the invention comprises joining a plurality of partstogether via use of the shape memory materials. Here, the parts arejuxtaposed so that at least one joint or joinder area is formed. Apreformed shape memory material such as a shape memory polymer isprovided and activated. The shape memory material is then applied to thejoint or joinder area and deformed into a desired shape. The shapememory material is deactivated while maintaining it in its deformedshape. The deformed shape is then bonded to the joint area to effectjoinder of the parts together.

Epoxy SMP

Generally, shape memory polymers (SMPs) are comprised of two essentialcomponents; the back bone polymer, which is comprised of monomericconstituents that undergo polymerization to produce polymers possessingspecific glass transition temperatures (T_(g)s), and a crosslinkingagent. The mixture of monomers can be formulated so that the glasstransition temperatures can be tuned to meet different operational needsfor specific applications.

In general, shape memory polymer (SMP) can be made with any polymersystem by introduction of a small, but specific amount of crosslinkingagent into the material. However, the exact chemistry to introduce thiscrosslinking into the material varies with different polymers. In thecase of epoxy SMP, this can be achieved by using amine and phenolreagents that form linear polymer chain with the diepoxide (e.g.Bisphenol A diglycidyl ether, which is the most commonly available epoxyresin) and cured with small amount of crosslinking multifunctionalamine, phenol or glycidyl ether reagents. In contrast, common epoxyresins are normally cured with stoichiometric amount of diaminecrosslinking reagents. The use of these amine reagents ensures there isenough flexibility between the crosslinking points within the polymermaterials, and this flexibility or mobility is what imparts thematerials with shape memory properties.

The crosslink density is crucial in controlling the elongation andtransition temperature (“T_(g)”) of epoxy SMP. For most applications,the highest crosslink density possible is desired in order to maximizethe T_(g) and thereby the use of the material. A relatively lowcrosslink density is required in SMP materials to allow movement ofepoxy chains, increasing elongation and shape memory properties.However, if too few crosslinkers are present, the material behaves as athermoplastic, irreversibly deforming at elevated temperatures.Therefore one must be careful to find the optimum crosslink density thatallows for maximum elongation with full retention of original form.

Crosslink density is defined as the number of moles of crosslinkerdivided by the total moles of the resin system. In formulation, balancedstoichiometry must be used, meaning that all reactive epoxide groupsmust have one active amino-hydrogen or phenolic-hydrogen to react with.Therefore, the monomers containing two active amino-hydrogen orphenolic-hydrogen serve as chain extenders while themultifunctional-amines, phenols, or glycidyl ethers serve ascrosslinkers. In formulation, two equations must be solvedsimultaneously: one balancing all reactive groups and the other definingthe crosslink density. Depending on the curing agents and epoxies used,crosslink densities ranging from 0.2 mol % to 10 mol % based on totalnumber of moles.

Dissolving thermoplastics in epoxy resins is often performed to increasetoughness. Often, solvents or kneading machines are used to adequatelyblend thermoplastics and epoxy resins. One approach that can be takenwith epoxy SMP is in situ polymerization, where a thermoplastic modifieris polymerized during the cure of the epoxy resin. The thermoplasticpolymerizes via a free-radical addition mechanism, while the epoxypolymerizes in an epoxide ring-opening reaction. This allows simplemixing of the two low viscosity resins: the thermoplastic monomers andthe epoxy resin system. The T_(g) of the original epoxy formulation isaffected depending on the thermoplastic used and degree ofpolymerization. Styrene and acrylate monomers can used together andindependently to tailor the T_(g) of the material. The loading ofinitiator can also be modified to control the chain length of thethermoplastic molecules. The presence of the thermoplastic phase doesnot hinder the elongation of the epoxy matrix. Any loading is possible,although visible phase separation occurs above 10 weight percent forpolystyrene systems.

All reagents that used to produce the epoxy-based SMP are commerciallyavailable; some are available in bulk scale. Some examples of reagentsare as follows.

Amine reagents can be 2-amino-3-picoline, 2-amino-6-picoline,2-aminopyridine, 3-aminopyridine, 4-aminophenol, 2-aminothiazole,8-aminoquinoline, 8-naphthylamine, ethanolamine, o-anisidine,2′-(2-aminoethoxy)ethanol, benzylamine, or propylamine, piperazine andsubstituted piperazines, e.g., 2-(methylamido)piperazine,2-methylpiperazine, 2,5-dimethylpiperazine, 2,6-dimethylpiperazine,aniline and substituted anilines, e.g., 4-(methylamido)aniline,4-methoxyaniline (p-anisidine), 3-methoxyaniline (m-anisidine),2-methoxyaniline (o-anisidine), 4-butylaniline, 2-sec-butylaniline,2-tert-butylaniline, 4-sec-butylaniline, 4-tert-butylaniline,5-tert-butyl-2-methoxyaniline, 3,4-dimethoxyaniline,3,4-dimethylaniline; alkyl amines and substituted alkyl amines, e.g.,propylamine, butylamine, tert-butylamine, sec-butylamine, benzylamine;alkanol amines, e.g., 2-aminoethanol and 1-aminopropan-2-ol; andaromatic and aliphatic secondary diamines, e.g.,1,4-bis(methylamino)benzene, 1,2-bis(methylamino)ethane andN,N′-bis(2-hydroxyethyl)ethylenediamine, N,N′-dibenzylethylenedimaine;and other aromatic amines, e.g., 2-aminobenothiazole,3-amino-5-methylpyrazole, 2-amino-6-methylpyridine, 3-aminophenol,2-amino-3-picoline, 4-aminopyridine, 3-aminopyridine, 2-aminpyridine,3-aminoquinoline, 5-aminoquinoline, 2-aminothiophenol.

Multifunctional cross-linking reagents can beBis-(4-glycidyloxyphenyl)methane (Bisphenol F),diglycidyl-1,2-cyclohexanedicarboxylate, resorcinol diglycidyl ether, orN,N-diglycidylaniline, tris(2,3-epoxypropyl) isocyanurate, glycerolpropoxylate triglycidyl ether, 3,5-diethyltoluene-2,4-diamine and3,5-diethyltoluene-2,6-diamine, methylenedianiline, diethylenetriamine,and tris(2-aminoethyl)amine.

In addition to using reagents containing active amino groups, it is alsopossible to use diphenol reagents containing active phenolic groups toproduce epoxy-based SMP, some examples of these diphenol reagents are asfollows: Hydroquinone, methylhydroquinone, resorcinol, catechol,4,4′-(9-fluorenylidene)diphenol, 2,7-dihydroxynaphthalene and bisphenolA.

In addition it is possible to tune the mechanical properties such astoughness and T_(g) of the epoxy SMP using thermopolastic.Thermoplastics are dissolved in epoxy resin systems to increasetoughness, enhance self-healing properties, and modify other materialproperties. By incorporation the following commercial thermoplastics inepoxy SMP resin the mechanical and chemical properties of the final SMPcan be tailored to specific design and environmental requirements:polystyrene, polysulfone, and polymethyl methacrylate. The followingthermoplastics, and their copolymers, also have potential use in epoxySMP: Polyacrylonitrile, Polybutylacrylate, Polymethylmethacrylate,Polybutadiene, Polyoxymethylene (acetal), High impact polystyrene,Polyamide, Polybutylene terephthalate, Polycarbonate, Polyethylene,Polyethylene terephthalate, Polyetheretherketone, Polyetherimide,Polyethersulfone, Polyphthalamide, Polyphenylene ether, Polyphenylenesulfide, Polystyrene, Polysulfone, Polyurethane, Polyester, andPoly(styrene-acrylonitrile).

The current material system shows a great degree of strain (i.e.elongation) above T_(g) as compared to those epoxy system that werepublished. The materials also show good stability significantly at least60° C. above T_(g), unlike the published material system which continuesto cure above T_(g) which leads to change of material properties eachtime the material is heated.

Several samples of the epoxy-based SMP were prepared, using eitheraniline, aminoethanol, p-anisidine, m-anisidine, 3-aminopyridine,4-tert-butylcatechol, resorcinol, hydroquinone, bisphenol A as thereagents to react with methylenedianiline and bisphenol A diglycidylether. For aniline-based epoxy SMP, crosslinker content from about 0.5mol % to 10 mol % was formulated.

The invention will now be further described with reference to a numberof specific examples which are to be regarded solely as illustrative andnot as restricting the scope of the invention.

Example 1

As an example, 1.08 g aniline (amine reagent) was mixed with 0.066 g ofmethylenedianline (crosslinking diamine). The resulting solution wasmixed with 4.17 g of bisphenol A diglycidyl ether to form an homogeneoussolution. This solution was then injected into a glass mold, made withtwo, 2″×2″ glass with a Viton O-ring sandwiched in between, by syringe.The resulting material was cured in an oven pre-heated to 125° C. for 18hours. This resulted in a clear solid shape memory polymer at roomtemperature that has a glass transition temperature (Tg) of about 104°C. The resulting material was also tough, as revealed by its resistanceto cutting by razor blade hitting with a hammer, and with largeelongation above its T_(g), and excellent shape recovery. The rubberymodulus of this material was also significantly higher than thestyrene-based SMP.

Example 2

For a resin system with a T_(g) of 103° C., Bisphenol A diglycidyl etherat 78.94% weight is mixed with aniline at 19.88% weight and DETDA (majorisomers: 3,5-diethyltoluene-2,4-diamine and3,5-diethyltoluene-2,6-diamine) at 1.19% weight. All components aremiscible liquids and are easily combined through mechanical mixing.

Example 3

For a resin system with a T_(g) of 60° C., diglycidyl ether of BisphenolA at 45.32% weight and 1,4-butanediol diglycidyl ether at 31.38% weightare mixed with aniline at 21.99% weight and DETDA (major isomers:3,5-diethyltoluene-2,4-diamine and 3,5-diethyltoluene-2,6-diamine) at1.31% weight. All components are miscible liquids and are easilycombined through mechanical mixing.

While the amount of crosslinking reagents used can vary from 0.01 mol %to 10 mol % or more, it is particularly preferred to keep the amountbetween 0.2 mol % to 7.0 mol %. The amount of phenol or amine reagentswill vary stoichiometrically with the epoxide reagents and each can varyfrom 35 mol % to 65 mol %. It is particularly preferred that both are inthe range of 45 mol % to 55 mol %.

The glass transition temperature of the shape memory polymer can be alsobe tailored by altering the mixture of mono- and multi-functional aminereagents and the multifunctional epoxy resins. The transitiontemperature can also be tailored by the combination of differentreagents and resins such that more than one reagent or resin is added toa single mixture. The resulting formulations all showed the ability towithstand strains from at least from 0-60% of their original size beforecritical deformation occurred. Additionally, some formulations showedthe ability to expand 0-700% of their original size before criticaldeformation occurred.

Finally, additional catalytic elements may be used to assist thereaction and lower the final cure temperature of the epoxy-based SMP.Some catalysts that could be used are: bis(triphenylphosphoranylidene)ammonium chloride, bis(triphenylphosphoranylidene) ammonium bromide, andbis(triphenuylphosphoranylidene) ammonium acetate.

The shape memory phenomenon in the vicinity of T_(g) and the ability toset the value of T_(g), by varying the composition, over a very broadrange of temperatures allows contemplation of numerous applications invaried uses including, but not limited to, molds for contact lensesmanufacturing, molds for composite manufacturing, structural deploymentdevices for remote systems, games and toys, domestic articles, arts andornamentation units, medical and paramedical instruments and devices,thermo-sensitive instruments and security devices, office equipment,garden equipment, educative articles, tricks, jokes and novelty items,building accessories, hygiene accessories, automotive accessories, filmsand sheets for retractable housings and packaging, coupling material forpipes of different diameters, building games accessories, folding games,scale model accessories, bath toys, boots and shoes inserts, skiingaccessories, suction-devices for vacuum cleaners, pastry-makingaccessories, camping articles, adaptable coat hangers, retractable filmsand nets, sensitive window blinds, isolation and blocking joints, fuses,alarm devices, sculpture accessories, adaptable hairdressingaccessories, plates for braille that can be erased, medical prosthesis,orthopedic devices, furniture, deformable rulers, recoverable printingmatrix, formable casts/braces, shoes, form-fitting spandex, form-fittingclothes, self-ironing clothes, self-fluffing pillows, deployablestructures, space deployable structures, satellites, and pipereplacements for underground applications.

Although this invention has been described with respect to certainpreferred embodiments, it will be appreciated that a wide variety ofequivalents may be substituted for those specific elements shown anddescribed herein, all without departing from the spirit and scope of theinvention as defined in the appended claims.

1. A product comprising: a thermo-reversible dry adhesive comprising: afirst layer comprising a dry adhesive; a second layer comprising a shapememory polymer; wherein the thermo-reversible dry adhesive has a firstshape at a first temperature and a second shape at a second temperaturewith a load applied.
 2. The product of claim 1, wherein the dry adhesivecomprises a soft dry adhesive.
 3. The product of claim 1, wherein theshape memory polymer comprises a shape memory polymer foam comprising atleast one of an epoxy, a polyurethane or a crosslinked vinyl polymer. 4.A product as set forth in claim 1 wherein the shape memory polymercomprises: at least one of a rigid epoxy or a flexible epoxy; and atleast one of a crosslinking agent or a catalytic curing agent; whereinthe rigid epoxy is an aromatic epoxy having at least two epoxide groups,the flexible epoxy is an aliphatic epoxy having at least two epoxidegroups, and the crosslinking agent is one of a multi-amine, an organicmulti-carboxylic acid, or an anhydride.
 5. A product as set forth inclaim 2, wherein the soft dry adhesive comprises: at least one of arigid epoxy or a flexible epoxy; and at least one of a crosslinkingagent or a catalytic curing agent; wherein the rigid epoxy is anaromatic epoxy having at least two epoxide groups, the flexible epoxy isan aliphatic epoxy having at least two epoxide groups, and thecrosslinking agent is one of a multi-amine, an organic multi-carboxylicacid, or an anhydride.
 6. A product as set forth in claim 1 furthercomprising at least one substrate wherein the thermo-reversible dryadhesive is positioned on top of the at least one substrate with thefirst layer in contact with the at least one substrate.
 7. A product asset forth in claim 6 wherein the pull-off force of the thermo-reversibledry adhesive with the curved structure is about 0 to 50 N/cm2 for one ofthe at least one substrate.
 8. A product as set forth in claim 6 whereinthe pull-off force of the thermo-reversible dry adhesive with therelatively flat structure is about 10 to about 200 N/cm2 for one of theat least one substrate.
 9. A product as set forth in claim 1 wherein theat least one substrate comprises at least one of an automotive body trimpiece, a sign, a picture, an automotive side molding, or a surfacedecorative film.
 10. A product as set forth in claim 9 wherein the atleast one substrate comprises one of stainless steel, glass, aluminumalloy 5657, polypropylene, or Teflon.
 11. A product as set forth inclaim 1, wherein the dry adhesive is grafted to the shape memory polymerto form a single layer.
 12. A method comprising: providing athermo-reversible dry adhesive comprising at least one dry adhesivelayer and at least one shape memory polymer layer; heating thethermo-reversible dry adhesive to a temperature higher than the glasstransition temperature of the shape memory polymer layer; imposing aload on the thermo-reversible dry adhesive while cooling to atemperature below the glass transition temperature of the shape memorypolymer layer, so that the dry adhesive layer substantially conforms toa corresponding topography of an underlying substrate to form a strongadhesive bond to the underlying substrate; and releasing thethermo-reversible dry adhesive from the underlying substrate by heatingthe thermo-reversible dry adhesive to a temperature above the glasstransition temperature of the shape memory polymer to cause the shapememory polymer to revert to its original shape, therein causing the dryadhesive layer to return to its original shape.
 13. A method as setforth in claim 12 wherein the load is about 1 N/cm2 to about 20 N/cm2.14. A method as set forth in claim 12 wherein the glass transitiontemperature of the shape memory polymer is about 25 to about 200° C. 15.A method as set forth in claim 12 wherein the glass transitiontemperature of the dry adhesive is about −90 to about 200° C.
 16. Amethod comprising: forming a thermo-reversible dry adhesive comprising:forming a first layer by curing a first component, a second component,and a third component; forming a second layer over the first layercomprising pouring a mixture of a fourth component and a fifth componentover the first layer and curing the second layer; and post-curing thefirst and second layers to form the thermo-reversible adhesive having acurved structure at a first temperature and having a relatively flatstructure at a second temperature with a load applied.
 17. A method asset forth in claim 16 wherein the first component, the second component,and the third component comprise: at least one of a rigid epoxy or aflexible epoxy; and at least one of a crosslinking agent or a catalyticcuring agent; wherein the rigid epoxy is an aromatic epoxy having atleast two epoxide groups, the flexible epoxy is an aliphatic epoxyhaving at least two epoxide groups, and the crosslinking agent is one ofa multi-amine, an organic multi-carboxylic acid, or an anhydride.
 18. Amethod as set forth in claim 16 wherein the first component, the secondcomponent, and the third component comprise an aromatic diepoxy, analiphatic diepoxy, and a diamine.
 19. A method as set forth in claim 18,wherein the aromatic diepoxy comprises diglycidyl ether of bisphenol Aepoxy monomer with an approximate epoxy equivalent weight of 180;wherein the aliphatic epoxy comprises NGDE; and wherein the diaminecomprises poly(propylene glycol)bis(2-aminopropyl)ether with an averagemolecular weight of
 230. 20. A method as set forth in claim 16, whereinthe fourth component and the fifth component comprise an aliphaticdiepoxy and a diamine, and wherein the components are present in anamount sufficient to provide, upon curing of the second layer, a softepoxy dry adhesive layer having a glass transition temperature of −90°C. to 200° C. and having a pull-off strength of 1-200 N/cm2.